Recalibration of phonetic categories by lipread speech: measuring aftereffects after a 24-hour delay.

Listeners hearing an ambiguous speech sound flexibly adjust their phonetic categories in accordance with lipread information telling what the phoneme should be (recalibration). Here, we tested the stability of lipread-induced recalibration over time. Listeners were exposed to an ambiguous sound halfway between /t/ and /p/ that was dubbed onto a face articulating either /t/ or /p/. When tested immediately, listeners exposed to lipread /t/ were more likely to categorize the ambiguous sound as /t/ than listeners exposed to /p/. This aftereffect dissipated quickly with prolonged testing and did not reappear after a 24-hour delay. Recalibration of phonetic categories is thus a fragile phenomenon.